1. Field of the Invention
The present invention relates to a method for manufacturing a magnetoresistive effect (MR) element, to a method for manufacturing a thin-film magnetic head with an MR element, and to a thin-film magnetic head with an MR element.
2. Description of the Related Art
As hard disk drive apparatuses (HDD) increase in capacity and reduce in size, highly sensitive and high-output thin-film magnetic heads are being demanded. In order to satisfy the demand, performance of giant magnetoresistive effect (GMR) thin-film magnetic heads with GMR read head elements are being improved. On the other hand, tunnel magnetoresistive effect (TMR) thin-film magnetic heads with TMR read head elements having a magnetoresistivity ratio more than twice as high as that of the GMR thin-film magnetic heads are being developed.
TMR thin-film heads differ from conventional GMR thin-film magnetic head in head structure because of the difference in the flowing direction of sense current. The head structure in which sense current flows in a direction parallel to the layer planes or film planes as in typical GMR thin-film heads is called as CIP (Current In Plane) structure, whereas the structure in which sense current flows in a direction perpendicular to the film planes as in TMR thin-film magnetic heads is called as CPP (Current Perpendicular to Plane) structure, respectively.
In fabrication of a GMR thin-film magnetic head with the CPP structure or a TMR thin-film magnetic head, it is important to ensure the flatness of a lower shield layer or lower electrode layer and an upper shield layer or upper electrode layer in order to improve the stability of the MR element.
The applicants of this application have proposed a method for manufacturing a thin-film magnetic head, having a step of depositing an MR multi-layer, a step of patterning the deposited MR multi-layer by milling with a mask to form an MR multi-layered structure, a step of depositing an insulation layer on a cap layer and a lower electrode layer at the top of the formed MR multi-layered structure, a step of planarizing the deposited insulation layer until the cap layer of the MR multi-layered structure is exposed, and a step of forming an upper electrode layer on the planarized insulation layer and MR multi-layered structure (U.S. Pat. No. 6,669,983 B2).
The manufacturing method described in U.S. Pat. No. 6,669,983 B2 is advantageous in that the upper electrode layer can be planarized. However, in general, it is necessary that the cap layer of the MR multi-layered structure is considerably thick because this layer is planarized by milling or chemical-mechanical polishing (CMP).
If the cap layer is thick, the profile of the MR multi-layered structure (cross section parallel to the air bearing surface (ABS)) will be trapezoidal in shape and accordingly the width (along the track width) of the magnetization free layer (free layer) will broaden.
This problem will be described below with reference to FIGS. 1a to 1e. If the cap layer 11a of the MR multi-layered structure 11 is thin, the width of the free layer 11b can be maintained narrow after the ion milling using a photoresist mask 10 to pattern the MR multi-layered structure 11 as shown in FIG. 1a. However, if the cap layer 11a′ of the MR multi-layered structure 11′ is thick, the width of the free layer 11b′ is significantly broadened as shown in FIG. 1b. This is because the widths of the masks 10 and 10′ are defined by the minimum line width determined by the physical limitation of lithography and cannot be reduced below the minimum line width. In other words, if the cap layer 11a′ is thick as shown in FIG. 1c, the upper electrode layer can be planarized by adequate CMP and the hard bias layer for magnetic domain control 12′ in the free layer can be made thick. Therefore a sufficient magnetic bias for magnetic domain control can be provided. However, the width of the free layer 11b′ broadens.
In contrast, if the cap layer is thin, the width of the free layer 11b can be made narrow but a sufficient bias for magnetic domain control cannot be provided because the hard bias layer 12 for magnetic domain control in the free layer is thin. If the thickness of the hard bias layer 12 is increased as shown in FIG. 1d and CMP is omitted in order to provide a sufficient bias for magnetic domain control, the upper electrode layer cannot be planarized. If CMP is applied to a degree that can be performed on the thin cap layer in order to planarized the upper electrode layer, the hard bias layer 12″ becomes thin as shown in FIG. 1e and therefore a sufficient bias for magnetic domain control cannot be provided.
In this way, there is a tradeoff among narrowing the width of the free layer, achieving a sufficient bias for magnetic domain control, and sufficiently planarizing the upper electrode layer.